AB0745 [18F]-FDG PET/CT IN LARGE VESSEL VASCULITIS: SEMI-QUANTITATIVE [18F]-FDG PET/CT ANALYSIS AND CORRELATION WITH DISEASE ACTIVITY
Authors: P. Fraticelli, G. Ghirelli, M. Pasquinelli, V. Maurizi, P. Pettinari, C. Cottignoli, F. M. Fringuelli, C. Romagnolo, N. Schicchi, L. Burroni, G. Moroncini
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> [18F]-FDG PET/CT in a useful tool to assist diagnosis and therapy of large vessel vasculitis (LVV). Visual grading methods are commonly used in clinical practice, but these may lead to interpretation mistakes because of the confounding factors due to atherosclerosis and basal setting of the exam, reducing diagnostic accuracy for detecting active disease. Therefore, a semi-quantitative analysis based on normalization of the arterial wall uptake to the background activity or grading the arterial inflammation against a reference background, were introduced in the context of clinical studies in the last years. <h3>Objectives</h3> To review a series of [18F]-FDG PET/CT of LVV by applying a semi-quantitative analysis that included the standardized uptake value (SUV) and a target-to-background ratio (TBR) to evaluate possible correlations between FDG uptake, considering also a TBR cut-off, haematological inflammatory markers and the CT angiography (CTA) findings. <h3>Methods</h3> We reviewed our internal database for [18F]-FDG PET/CT among patients with LVV (GCA, Takayasu). Were selected [18F]-FDG PET/CT with available blood inflammatory markers and a CTA performed during the same period (permitted a range of 7 days for blood tests or 30 days for CTA), patients were all out of therapy or on stable therapy. As controls were taken ten patients undergoing PET/CT for oncologic diagnostics. The SUV maximum (SUV max) was considered that in the aortic arch or in the vascular region with higher levels of SUV. Target-to-background ratio was calculated considering average SUV in the right hepatic lobe (SUV max/SUV liver ratio). Non parametric test for correlation analysis were performed between SUV max, SUV max/SUV liver ratio and CRP (mg/dl). According previous data a cut-off of SUV max/SUV liver ratio &gt;1.2 was considered and was then compared with CRP, for disease activity, and with CTA, to find agreement with vessel wall thickness and contrast enhancement. <h3>Results</h3> 33 [18F]-FDG PET/CT from 21 patients, 4 Takayasu and 17 GCA, 9M/12F, mean age 61,2 years were available for analysis, 13 out of them had at least one CTA to compare (total 21 CTA). SUV max and SUV max/SUV liver ratio in LVV resulted statistically higher than controls (Mann-Whitney test respectively U= 21, p = 0.00001 and U=76, p=0.027). Linear correlation between SUV max and CRP resulted highly significant (Spearman: r= 0,51 p = 0,006) but also correlation for SUX max/SUV liver ratio resulted significant (Spearman: r = 0,47, p = 0,011). Applying a cut-off for SUV max/SUV liver &gt;1,2 we found a statistically significant agreement with CRP (Mann-Whitney U=43 p =0.0015). Less correlation was found when [18F]-FDG PET/CT SUV was compared with contrast enhancement and vessel wall thickening of CTAs, probably, because of the increased vessel thickness remains even in the inactive disease stages. <h3>Conclusion</h3> Although further studies are expected, semi-quantitative [18F]-FDG PET/CT scoring methods and simple cut off scores based on TBR analysis seems to correlate with disease activity and they could be used in the clinical practice, together with inflammation indices and other radiological imaging techniques, to offer a reliable and repeatable tool to help clinicians in managing LVV. <h3>References</h3> [1]<b>FDG-PET/CT(A) imaging in large vessel vasculitis and polymyalgia rheumatica: joint procedural recommendation of the EANM, SNMMI, and the PET Interest Group (PIG), and endorsed by the ASNC.</b> Slart RHJA; Writing group; Reviewer group; Members of EANM Cardiovascular; Members of EANM Infection &amp; Inflammation; Members of Committees, SNMMI Cardiovascular; Members of Council, PET Interest Group; Members of ASNC; EANM Committee Coordinator. <i>Eur J Nucl Med Mol Imaging</i>. 2018;45(7):1250-126 [2]<b>Diagnostic value of [18F]FDG-PET/CT for treatment monitoring in large vessel vasculitis: a systematic review and meta-analysis.</b> van der Geest KSM, Treglia G, Glaudemans AWJM, Brouwer E, Sandovici M, Jamar F, Gheysens O, Slart RHJA. <i>Eur J Nucl Med Mol Imaging.</i> 2021;48(12):3886-3902. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.